Dump trucks, used for carrying crushed stones in mines or etc., have been provided as supersized work vehicles. Compared to vehicles such as normal trucks, dump trucks of this type have a remarkably large vehicle width and a large longitudinal length. Therefore, it is difficult for operators thereof to grasp surrounding statuses by means of side mirrors and etc. In view of this, as described in U.S. Patent Application Publication No. US 2009/0259400 A1, for instance, a perimeter monitoring system is provided for efficiently checking the surrounding status of a vehicle.
The system disclosed in the above mentioned publication includes an obstacle detection system, an operator interface, an interface module and a controller connected to these components. When an obstacle is detected, the system is configured to display such dangerous obstacle on a display device and issue a warning to an operator.
On the other hand, Japan Laid-open Patent Application Publication No. JP-A-2010-198519 describes a device configured to present a risk of an obstacle within an active positional range of a working unit. It is herein detected whether or not an obstacle exists in the surrounding of a working machine. When an obstacle exists, a positional relation between a working machine main body and the obstacle is computed, and further, a risk level of making contact with the obstacle is computed based on an operational action of the working machine. Then, alert contents are configured to be outputted to a monitor and an audio output device in accordance with the risk.